THE LATTICE LOCATIONS OF SILICON IMPURITIES IN GAAS - EFFECTS DUE TO STOICHIOMETRY, THE FERMI ENERGY, THE SOLUBILITY LIMIT AND DX BEHAVIOR

An outline of infrared localized vibrational mode absorption spectroscopy relevant to silicon impurities in GaAs is presented. Absorption lines from Si(Ga) donors, Si(As) acceptors, Si(Ga)-Si(As) pairs, Si(Ga)-V(Ga) (Ga vacancy) pairs and a complex Si-X (involving Si(As) and V(Ga)) have been identified as well as lines from Si(Ga)-Cu(Ga), Si(Ga)-H, Si(As)-H and Si(Ga)-B(As) pairs. These observations are related to the electrical properties of n-type Bridgman, liquid-encapsulated Czochralski and molecular beam epitaxial (MBE) (001) GaAs, and to p-type liquid phase epitaxial and MBE (111)A layers. The discussion relates to dynamic site switching, effects due to counter-doping with shallow acceptors, the solubility of silicon, and DX behaviour observed in homogeneously doped material and proposed for delta-doped MBE (001) layers. The major problem is to understand the processes that limit the maximum carrier concentration that can be achieved in n-type crystals.